My view point is likely skewed because I did a sturgian playthrough and there are fewer villages which are much more dispersed, so I was only able to keep maybe 10-20% of my troops as nobles. I'm sure in battania where there is a mass of villages it was extremely OP (i'd bet vlandia is somewhere in the middle).While I do agree with this, I have to say that it was unbalanced in 1.5.6. I started a campaign where I was able to get 50 Vlandian Knights before day 100 (I got the perk which gives an extra recruiting slot).
I would love to see some kind of notables in castles giving access to noble troops.
Personally I think these % of powerful notables needs to be different in each of the factions due to their general locations. Battannia needs a small % compared to Sturgia or Aserai who would need a higher percent. Even a blanket every faction has 20% notables who are powerful impacts each faction very differently.
I made this image for another purpose but it fits here too to emphasize my point and Batannias advantage. Batannia would have 22 powerful nobles in the same area that Sturgia would only have 11. If Sturgia's percent was 40% we be much more even with 21 powerful notables for Sturgia.
The red circles in this image are the same size.
I agree the adding noble line notables at castles would be great, even if it was just 1 or 2 notables, but we'd still have the same distribution issue.